1. Field of the Invention
The present invention relates to an electrostatic chuck for clamping a semiconductor substrate, a glass substrate, or the like.
2. Description of Prior Art
An electrostatic chuck as shown in Documents 1-4 has been used as a means for clamping and retaining a semiconductor substrate or a glass substrate within a plasma processing chamber where etching, CVD, sputtering, ion implantation, ashing, or the like are performed.
The conventional electrostatic chuck as shown in Documents 1-2 has a structure where a dielectric layer 103 having an electrode 102 inside is attached in an integrated manner onto a metal plate 100 by using an organic adhesive 101 such as a silicone resin. As a method for placing the electrode 102 inside the dielectric layer 103, an electrode (tungsten) is printed on a surface of a ceramic green sheet which becomes a dielectric layer after being fired, and another ceramic green sheet is laminated thereon and fired (hot pressing).
Document 1: Japanese Utility-Model Application Publication No. 4-133443
Document 2: Japanese Patent Application Publication No. 10-223742
Document 3: Japanese Patent Application Publication No. 2003-152065
Document 4: Japanese Patent Application Publication No. 2001-338970
Residue and product material from a semiconductor wafer or a coating film attach to the inner surface of the chamber after plasma processing is performed. Further, as plasma processing is repeated, the residue and product material are gradually accumulated, and finally break off from the inner surface of the chamber. They attach to a surface of a semiconductor substrate or a glass substrate, which results in deterioration of the yield.
Thus, according to the conventional art, the inside of the chamber is regularly cleaned by plasma so as to remove the residue and product material attaching to the inner surface of the chamber. In this instance, according to the conventional art, in order to prevent a surface of the electrostatic chuck from being exposed to plasma, cleaning is performed in a state where the surface of the electrostatic chuck is covered with a dummy wafer. However, these days, a surface of an electrostatic chuck is directly exposed to cleaning plasma such as O2 gas or CF4 gas without covering the surface of the electrostatic chuck with a dummy wafer so as to reduce the tact time and improve the production efficiency. This is referred to as waferless plasma cleaning, and this is the recent trend of the industry.
The average grain size of an electrostatic chuck made of common ceramic ingredient powder is 5-50 μm after being fired. If such an electrostatic chuck undergoes the above-mentioned waferless plasma cleaning, the average roughness (Ra) is increased due to release of grains from the surface of the electrostatic chuck and corrosion of the boundary, which results in deterioration of the electrostatic clamping force and deterioration of the heat transfer coefficient at the solid contact boundary face. Consequently, the electrostatic chuck needs to be replaced early.
In order to solve the above-mentioned problems, Document 3 has disclosed an electrostatic chuck in which the average size of the ceramic is reduced to be 2 μm or less. However, in order to incorporate an electrode inside a dielectric layer, a conventional electrostatic chuck requires technically high and complicated processes for integrating two dielectric substrates in a state where an electrode material is interposed therebetween by heat and pressure processing such as hot pressing after the two dielectric substrates are fired and formed. Consequently, there are drawbacks that the reliability is deteriorated and the processing time is increased.
The above-mentioned ceramic dielectric substrate in which the average grain size is reduced to be 2 μm or less cannot be obtained by firing laminated green sheets in a state where an electrode is interposed therebetween because there is a problem with removing a binder at the time of firing. Specifically, in order to produce a conventional electrostatic chuck having plasma-resistance, a technique for incorporating an electrode inside a dielectric layer substrate which has been fired is required.
In order to solve the above-mentioned problem, Document 4 has disclosed a method comprising the steps of forming an electrode on a surface of a dielectric layer substrate, attaching an insulating resin such as polyimide thereonto, and bonding it to a metal base plate. However, this structure has drawbacks of increase of the wafer temperature due to the low heat transfer coefficient of the insulating resin, and the reliability of the insulation.
The object of the present invention is to provide an electrostatic chuck which can be manufactured by a simple process, and has high resistance to waferless plasma cleaning, high capability of cooling a wafer, and high reliability of electrical insulation between the electrode and the metal plate so as to solve all the problems mentioned above.